In optical telecommunication networks, a photonic switching node (PSN), which is also known as a photonic cross-connect (PXC) or a photonic-switched wavelength-grooming network node, performs a primary function of routing an input optical signal to one or more output ports. The input optical signal may comprise one or more wavelength channels. A “wavelength channel” is an optical signal with a single wavelength. One example of multiple-wavelength optical signal is a dense wavelength division multiplexed (DWDM) signal. The PSN may route one of the wavelength channels and output an optical signal comprising the same wavelength channel. Through photonic switching, the PSN provides flexibility points in the network for traffic grooming, fiber protection, and wavelength conversion.
One prior art photonic switching node architecture is illustrated in FIG. 1. A same or similar architecture is described in U.S. patent application Ser. No. 10/286,781, entitled “Modular Photonic Switch with Wavelength Conversion,” filed Nov. 4, 2002, which is hereby incorporated herein in its entirety. As shown in FIG. 1, a typical multi-wavelength switch plane photonic network node (PSN) consists of a set of photonic switch fabric cards #1-#8 and multiple instances of photonic line cards #1-#16. The ingress and egress sides of the respective line card are shown separately, for the purpose of better illustration of the signal flow; although in reality each card contains ingress and egress part on it. Each ingress line card receives input signals comprising one or more wavelengths via a plurality of ingress optical network fibers 102, demultiplexes the input signals into wavelength channels (e.g., λ 1-4, λ 5-8, . . . λ 29-32, etc.), and feeds the different wavelength channels to corresponding switch fabric cards through an optical backplane 106. Each switch fabric card routes transparently an optical signal of certain wavelengths, through the optical backplane 106 for a second time, to an appropriate wavelength port of corresponding egress line cards. Each egress line card multiplexes a received optical signal with respective wavelengths and further transmits it through a plurality of egress optical fibers 104. The PSN shown in FIG. 1 can switch 16 instances of 32 wavelengths from one line card to another. Much larger PSNs (e.g., 640×640) with similar attributes have been demonstrated or built.
Another prior art system is described in U.S. patent application Ser. No. 09/726,027, entitled “Protection Switching Arrangement for an Optical Switching System,” filed Nov. 30, 2000, which is incorporated herein in its entirety.
To date, in long haul, optical access, and metro core applications, optical building blocks for photonic line cards have mostly been implemented with discrete components that are either stand-alone or co-packaged in a box. As the switching capacity of PSNs increases, the traditional approach can pose a number of problems. For example, as each discrete component has its own package and takes substantial space, the overall size of a photonic line card based on discrete components can be considerably large in terms of footprint. Furthermore, discrete components typically require additional optical interconnects among the components or functions. Such parasitic optical interconnects are almost always associated with extra cost, space, and deteriorating performance. As a result, a PSN based on discrete components can be bulky, expensive, hard to configure or reconfigure, and unreliable.
In view of the foregoing, it would be desirable to provide a solution for photonic switching which overcomes the above described inadequacies and shortcomings.